1. Field of the Invention
This invention relates to a decurling apparatus for decurling sheets of paper, and more particularly this invention relates to an apparatus for reducing sheet curl as induced, for example, by heat and pressure roll type fusers of the type typically employed in a xerographic or electrophotographic or analogous-type printing machines.
2. Description of the Prior Art
In the art of xerography, a photoconductor P/C generally comprising a photoconductive insulating material adhered to a conductive backing is charged uniformly. Then the P/C is exposed to a light image of an original document to be reproduced. The latent electrostatic images, thus formed, are rendered visible by applying any one of numerous pigmented resins specifically designed for this purpose. In the case of a reusable P/C, the pigmented resin, more commonly referred to as toner which forms the visible images is transferred to plain paper. After transfer, the toner images are made to adhere to the copy medium usually through the application of heat and pressure by means of a roll fuser.
One of the advances in the art of contact fusing of toner images is the nip forming roll fuser (i.e. a roll fuser wherein the nip between the rolls is formed by deforming the softer fuser roll) wherein a heated roll is provided with an outer deformable coating of silicon rubber, for example. A harder, usually non-heated, pressure roll is pressure engaged with the softer fuser roll to create a nip therebetween. Copy sheets having toner images electrostatically adhered thereto are passed through the nip with the images contacting the heated roll.
The requisite roll size is a function of a number of variables such as the copy making speed of the machine. Thus, the faster machines utilize relatively larger rolls whereas the slower machines use small (i.e. 11/2 to 2 inch diameter) diameter rolls. With the smaller rolls, the copy sheets release or fall away from the nip forming fuser roll thereby coming to rest on the pressure roll mounted beneath the fuser roll. This results in the copy sheet taking the general shape of the pressure roll. One such fuser arrangement was found to produce between 1/2 to 11/2 inch flat curl which bends away from the image. The copies in some cases form scrolls and can cause post fuser handling problems, in particular, with regard to the stacking of the copies in the output tray.
In addition to the fusing operation, as the sheet of support material passes through the various processing stations in, for example, an electrophotographic printing machine, a curl or bend is frequently induced therein. Occasionally, this curl or bend may be inherent in the sheet of support material due to the method of manufacture thereof. It has been found that this curl is variable from sheet to sheet within the stack of sheets utilized in the printing machine. The curling of the sheet of support material causes handling issues as the sheet is processed in the printing machine. Sheets delivered in a curled condition have a tendency to have their edges out of registration with the aligning mechanisms employed in the printing machine. In addition, curled sheets tend to frequently produce jams or misfeeds within the printing machine. This problem has been resolved by utilizing bars, rollers or cylinders which engage the sheet material as it passes through the printing machine. Frequently, belts or soft rollers are used in conjunction with a hard penetrating roll to remove the curl in a sheet. However, systems of this type have disadvantages. For example, the size of the de-curler is not necessarily consistent with that required in electrophotographic printing machines. In addition, decurlers of this type cannot decurl under stress conditions since they do not strain the sheets due to belt flexing.
Various approaches have been devised to improve sheet de-curlers such as described in the following prior art references:
U.S. Pat. No. 4,326,915
Patentee: Mutschler PA1 Issued: Apr. 27, 1982 PA1 Patentee: Bowler, Jr. PA1 Issued: Feb. 18, 1986 PA1 Patentee: Kuo, et al. PA1 Issued: May 27, 1986 PA1 Patentee: Wyer PA1 Issued: Dec. 9, 1986 PA1 Patentee: Hamada PA1 Issued: Aug. 17, 1993 PA1 Patentee: Wyer PA1 Issued: Dec. 14, 1993 PA1 Patentee: Bowler, Jr. PA1 Issued: Aug. 20, 1996 PA1 Patentee: Kuo, et al. PA1 Issued: Dec. 8, 1998
U.S. Pat. No. 4,571,054
U.S. Pat. No. 4,591,259
U.S. Pat. No. 4,627,718
U.S. Pat. No. 5,237,381
U.S. Pat. No. 5,270,778
U.S. Pat. No. 5,548,389
U.S. Pat. No. 5,848,347
The disclosures of the foregoing prior art patents can be briefly summarized as follows:
Mutschler (U.S. Pat. No. 4,326,915) describes an apparatus in which sheet material is decurled. The apparatus presses the sheet material into contact with a substantially rigid arcuate member in at least two regions. In this way, the sheet material moves about the arcuate member in a curved path to remove the curl therein.
Bowler, Jr. (U.S. Pat. No. 4,571,054) describes a post-fuser copy sheet decurler including means for reverse (i.e. direction opposite to bending caused by the pressure roll) bending of the copy sheets while they are in a plastic state, that is while the sheets are still at an elevated temperature.
Kuo, et al. (U.S. Pat. No. 4,591,259) describes an apparatus in which sheet material is decurled. The apparatus includes a baffle type decurler in which a sheet moving therethrough chooses one of three paths and baffles, depending on the direction and amount of curl. Spring loaded baffles in conjunction with idler rolls reverse bends the sheets in two of the three paths.
Wyer (U.S. Pat. No. 4,627,718) describes a sheet curl control apparatus that includes a pair of contacting rolls and a baffle extending across the path of a sheet exiting the nip between the rolls so as to deflect it about one of the rolls.
Hamada (U.S. Pat. No. 5,237,381) describes a sheet curl discharging apparatus having a curl generating device wherein a curl is generated in a sheet while the sheet is passing through the curl generating device, and a first guide disposed downstream of the curl generating device and switchingly movable between a first position where the sheet is directed toward a curved sheet path and a second position where the sheet is directed toward a direction the same as sheet feeding direction from the curl generating device. The apparatus further has a sheet discharge guide disposed between the curl generating device and the first guide and switchingly movable in synchronism with the switching movement of the first guide to change its posture, between a position where the sheet discharged from the curl generating device is curled reversely and a position where the sheet discharged from the curl generating device is not further curled.
Wyer (U.S. Pat. No. 5,270,778) describes a sheet curl control apparatus including a decurler for reducing the curl in sheet material passing therethrough and adjusting means coupled to the decurler for adjusting the decurling action of the decurler. Sensing means in the form of an infra-red emitter and two infra-red detectors are employed for sensing the extent of any residual curl left in the sheet material after it has passed through the decurler and for feeding a signal indicative of the residual curl to control means, conveniently including a stepper motor, for automatically adjusting the adjusting means, for example a rack and pinion arrangement, thereby to alter the decurling action of the decurler in a predetermined manner. The sheet curl control apparatus is described in relation to its use in a copier for duplex copying.
Bowler, Jr. (U.S. Pat. No. 5,548,389) describes a copy sheet decurling mechanism employed in conjunction with a heat and pressure fuser for reducing or eliminating the curl induced into the copy sheets by the fuser roll of the fuser. Stripper fingers, the position and/or angle of which can be selectively varied, are provided for reverse (i.e. direction opposite to bending caused by the pressure roll) bending of the copy sheets while they are in a plastic state, that is while the sheets are still at an elevated temperature.
Kuo, et al. (U.S. Pat. No. 5,848,347) describes a compact dual decurler mechanism that provides a single straight paper path for achieving bidirectional decurling capability consisting of two pairs of drive roll and pinch shaft and a camming mechanism for controlling their engagements. The first and second pairs are oriented in opposite directions. A first elastomer drive roll is disclosed.
In view of the current state of the prior art technology there exists a need to have an improved decurler, especially a decurler for use in a xerographic or electrophotographic printer that is able to decurl in the direction towards the image on the sheet as well as decurling in the direction away from the image on the sheet. Previously, this has been accomplished by using two separate decurlers, one for each curl direction. In addition, instead of the need for an expensive support structure for a decurler apparatus, there exist a need for a simple and relatively inexpensive decurler apparatus. In addition to these and all the other advantages of a decurler apparatus as referred to above, it would represent a very large advantage if the user of a xerographic or electrophotographic printer having a decurler apparatus as part of its finishing process could easily adjust the amount of decurling in the paper sheets. Accordingly, it is a primary advantage of this invention to provide a new and improved decurler apparatus for use in a printing machine such as a xerographic or electrophotographic printer which will exhibit all of the specific advantages referred to above.
Additional advantages of the invention will be set forth in part in the description which follows, and some will be obvious from the description, or may be learned by practice of the invention in accordance with various features and combinations as particularly pointed out in the appended claims.